The present invention generally relates to bond pads on a semiconductor structure and a method for forming the bond pads and more particularly, relates to bond pads on a semiconductor structure that are built with surrounding and spaced-apart heat dissipating rings for improving heat conductance and mechanical strength of the pads and method for forming such pads.
In the fabrication processes for semiconductor devices, an integrated circuit chip is frequently assembled in a package in a final process step to complete the fabrication process. The assembled package can then be connected to a printed circuit board as part as a large circuit. To establish an electrical communication with the integrated circuit chip, a wire bonding process is frequently used to connect a multiplicity of bond pads on the integrated circuit chip to the outside circuitry.
In a typical IC chip, active circuit elements such as transistors, resistors, etc., are positioned in the central portion, i.e., the active region, of the chip while the bond pads are normally arranged around the periphery of the active region such that active circuit elements are not likely to be damaged during a subsequent bonding process. When a wire bonding process is performed on a bond pad on an IC chip, the process normally entails the bonding of a gold or aluminum wire to the bond pad by fusing the two together with ultrasonic energy. The wire is then pulled away from the bond pad after the bond is formed. During the bonding of the gold wire to the pad and the pulling away of the wire from the pad, high mechanical stress is placed on the bond pad. When the bond pads are not properly formed, defects such as delamination have been encountered. This occurs due to the fact that during the attachment of a gold wire to a bond pad, a high level of mechanical stress is placed on the pad. It occurs when a relatively large, heavy bond is placed on top of layers which may not have strong adhesion to the underlying layers. For instance, one factor that may affect adhesion between the layers is the common usage of a diffusion barrier layer formed of a material such as TiN for preventing aluminum diffusion into underlying conductive layers during subsequent high temperature processes. The diffusion barrier layer utilized, i.e., TiN, TiW or other alloys, does not have strong adhesion to the underlying oxide layer in the bond pad. This is only one example that bond pad lift-off defect occurs. A lift-off problem frequently occurs at an interface between a polycide layer and a field oxide layer.
Other reasons may also cause bond pad lift-off or delamination problems in semiconductor devices. For instance, in more recently developed semiconductor devices wherein low dielectric constant (low-k) materials have been used which further cause adhesion problems between these low-k dielectric materials and the underlying oxide layers. The adhesion of low-k dielectric material, or inter-metal-dielectric (IMD) material to oxide is poorer than that of oxide to oxide. The use of low-k dielectric materials, such as HSQ (hydrogen silsesquioxane) and MSQ (methylsil sesquioxane) have been desirable in high performance semiconductor structures since due to their low-k characteristics, thinner layers of the materials may be utilized as insulating layers. Another drawback of these low-k dielectric materials is their low thermal conductivity when compared to that of regular oxide. During a chip bonding process, the local temperature around a bond pad is significantly higher due to the poor thermal conductivity of the low-k dielectric material. The thermal stress caused by the poor thermal conductivity of IMD, in addition to the mechanical stresses caused by the bonding operation, may cause delamination of the low-k IMD layers from their underlying oxide layers.
Others have attempted to solve the problems caused by the low-k IMD materials due to their poor thermal conductivity and poor adhesion to oxide. For instance, a plurality of via plugs have been used between metal bonding pads in order to improve heat conduction and film integrity. The use of multiple via plugs alleviates the thermal stress problem somewhat when compared to a single via plug since better heat conductance is achieved. The mechanical strength is also somewhat improved due to the anchoring capability of multiple via plugs which is better than that of a single via plug. However, the use of a plurality of via plugs between metal bonding pads alone is insufficient to prevent the delamination or thermal stress problems when low-k IMD materials are utilized in semiconductor structures.
It is therefore an object of the present invention to provide bond pads in a semiconductor structure that do not have the drawbacks or shortcomings of bond pads prepared by conventional methods.
It is another object of the present invention to provide bond pads in a semiconductor structure that have significantly improved thermal conductance and mechanical strength.
It is a further object of the present invention to provide bond pads in a semiconductor structure that are equipped with surrounding and spaced-apart heat dissipating rings.
It is another further object of the present invention to provide bond pads in a semiconductor structure that are equipped with heat dissipating rings which are fabricated during the same fabrication process for forming the bond pads.
It is still another object of the present invention to provide bond pads in a semiconductor structure that are equipped with heat dissipating rings which provide improved thermal conductance and mechanical anchoring capability.
It is yet another object of the present invention to provide bond pads equipped with heat dissipating rings which are formed of an upper conductive ring and a lower conductive ring of substantially the same shape connected thereinbetween by a plurality of dummy via plugs formed by a thermally conductive material.
It is still another further object of the present invention to provide a method for forming a heat dissipating ring around a bond pad for improving heat conductance and mechanical strength of the pad by photolithographically forming the heat dissipating ring simultaneously with the bond pad.
It is yet another further object of the present invention to provide a semiconductor structure that includes a bond pad that is substantially surrounded and insulated by a low-k IMD material layer and a heat dissipating ring surrounding the bond pad for improving thermal conductance and mechanical strength of the pad.
In accordance with the present invention, bond pads equipped with heat dissipating rings and a method for forming the bond pads are provided.
In a preferred embodiment, a semiconductor structure is provided which includes a pre-processed semiconducting substrate that has a dielectric material layer on top, a bond pad substantially surrounded and insulated by the dielectric material layer, the bond pad is formed of two metal layers and a plurality of metal via plugs connected thereinbetween, and a heat dissipating ring surrounding and spaced-apart from the bond pad, the heat dissipating ring is formed of an upper conductive ring and a lower conductive ring of substantially the same configuration connected therein between by a plurality of dummy via plugs formed of a thermally conductive material.
The semiconductor structure may further include a dielectric material layer on top of the structure that is formed of a low dielectric constant (low-k) material. The low-k material may be hydrogen silsesquioxane (HSQ) or methyl silsesquioxane (MSQ). The structure may further include a second heat dissipating ring positioned outside and spaced-apart from the heat dissipating ring. The thermally conductive material for forming the dummy via plugs may be a metallic material, for instance, a refractory metal, aluminum or copper. The plurality of dummy via plugs and the upper and lower conductive rings do not intercept any metal runners for the circuit formed in the semiconductor structure.
The present invention is further directed to a method for forming a heat dissipating ring around a bond pad for improving heat conductance and mechanical strength which can be carried out by the operating steps of providing a pre-processed semiconducting substrate hat has a first layer of inter-metal-dielectric (IMD) material on top, forming photolithographically a first metal pad and a first metal ring surrounding and spaced-apart from the first metal pad, depositing a second IMD layer on top of the first metal ring, forming photolithographically in the second IMD layer a first plurality of metal via plugs on the first metal pad and a second plurality of dummy via plugs on the first metal ring, depositing a third IMD layer on top of the first plurality of metal via plugs and the second plurality of dummy via plugs, and forming photolithographically in the third IMD layer a second metal pad connected to the first plurality of metal via plugs and a second metal ring connected to the second plurality of dummy via plugs, whereby the first metal pad, the second metal pad and the first plurality of metal via plugs connected thereinbetween form the bond pad surrounded by a spaced-apart heat dissipating ring formed by the first metal ring, the second metal ring and the second plurality of dummy via plugs connected thereinbetween.
The method for forming a heat dissipating ring around a bond pad may further include the step of depositing the first, the second and the third IMD layer with a high dielectric constant material. The method may further include the step of depositing the first, second, and third IMD layer with HSQ or MSQ. The method may further include the step of forming the first metal pad and the first metal ring by the same metal, the step of forming the first plurality of metal via plugs and the second plurality of dummy via plugs of the same metal, or the step of forming the first plurality of metal via plugs and the second plurality of dummy via plugs in a refractory metal, aluminum or copper. The method may further include the step of forming the second metal pad and the second metal ring in the same metal deposition process. In the method, the first metal ring, the second plurality of dummy via plugs and the second metal ring do not intercept metal runners for the bond pad.
The present invention is further directed to a bond pad equipped with a heat dissipating ring that includes a bond pad substantially surrounded and insulated by a layer of IMD material, the bond pad may be formed of two metal layers and a plurality of metal via plugs connected thereinbetween, and a heat dissipating ring surrounding and spaced-apart from the bond pad, the heat dissipating ring may be formed of an upper conductive ring and a lower conductive ring of substantially the same configuration connected thereinbetween by a plurality of dummy via plugs formed of a thermally conductive material.
In the bond pad equipped with a heat dissipating ring, the layer of IMD material may be a low dielectric constant material, or may be a HSQ or MSQ material. The heat dissipating ring anchors at least two dielectric material layers together achieving improved mechanical strength. The plurality of metal via plugs and the plurality of dummy via plugs may be formed of the same metal selected from the group consisting of refractory metals, aluminum and copper.